Messages in this thread | | | Date | Thu, 7 Jul 2022 11:53:50 +0100 | Subject | Re: [PATCH v2 1/4] PM: EM: convert power field to micro-Watts precision and align drivers | From | Lukasz Luba <> |
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On 7/7/22 11:53, Viresh Kumar wrote: > On 07-07-22, 08:15, Lukasz Luba wrote: >> The milli-Watts precision causes rounding errors while calculating >> efficiency cost for each OPP. This is especially visible in the 'simple' >> Energy Model (EM), where the power for each OPP is provided from OPP >> framework. This can cause some OPPs to be marked inefficient, while >> using micro-Watts precision that might not happen. >> >> Update all EM users which access 'power' field and assume the value is >> in milli-Watts. >> >> Solve also an issue with potential overflow in calculation of energy >> estimation on 32bit machine. It's needed now since the power value >> (thus the 'cost' as well) are higher. >> >> Example calculation which shows the rounding error and impact: >> >> power = 'dyn-power-coeff' * volt_mV * volt_mV * freq_MHz >> >> power_a_uW = (100 * 600mW * 600mW * 500MHz) / 10^6 = 18000 >> power_a_mW = (100 * 600mW * 600mW * 500MHz) / 10^9 = 18 >> >> power_b_uW = (100 * 605mW * 605mW * 600MHz) / 10^6 = 21961 >> power_b_mW = (100 * 605mW * 605mW * 600MHz) / 10^9 = 21 >> >> max_freq = 2000MHz >> >> cost_a_mW = 18 * 2000MHz/500MHz = 72 >> cost_a_uW = 18000 * 2000MHz/500MHz = 72000 >> >> cost_b_mW = 21 * 2000MHz/600MHz = 70 // <- artificially better >> cost_b_uW = 21961 * 2000MHz/600MHz = 73203 >> >> The 'cost_b_mW' (which is based on old milli-Watts) is misleadingly >> better that the 'cost_b_uW' (this patch uses micro-Watts) and such >> would have impact on the 'inefficient OPPs' information in the Cpufreq >> framework. This patch set removes the rounding issue. >> >> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> >> --- >> drivers/cpufreq/mediatek-cpufreq-hw.c | 7 ++-- >> drivers/cpufreq/scmi-cpufreq.c | 6 +++ >> drivers/opp/of.c | 15 ++++---- >> drivers/powercap/dtpm_cpu.c | 5 +-- >> drivers/thermal/cpufreq_cooling.c | 13 ++++++- >> drivers/thermal/devfreq_cooling.c | 19 ++++++++-- >> include/linux/energy_model.h | 54 +++++++++++++++++++-------- >> kernel/power/energy_model.c | 24 ++++++++---- >> 8 files changed, 100 insertions(+), 43 deletions(-) > > Acked-by: Viresh Kumar <viresh.kumar@linaro.org> >
Thank you Viresh for the ACKs!
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